HbA2 levels in normal adults are influenced by two distinct genetic mechanisms.

Using a genome-wide association study, we found that common inter-individual differences in haemoglobin A(2) (HbA(2) , α(2) δ(2) ) levels are largely governed by genetic factors (42% of variability). The influence of age (1%) and sex (4%) was small. HbA(2) levels were influenced by two loci: the HBS1L-MYB locus on chromosome 6q, which has been shown to have pleiotropic effects on other haematological traits; and a second locus surrounding HBB, the gene encoding β-globin. Our results suggest that HbA(2) levels in adults are influenced by two different biological processes: one via kinetics of erythropoiesis, and the other, via competition between HBB and HBD activity.